Analysis & Opinion

WASHINGTON (Reuters) - When U.S. Energy Secretary Steven Chu resigned on Friday, he singled out for praise a former governor who has worked to clean up nuclear waste, a move that raised Christine Gregoires' profile as a possibility for the Obama administration's energy and climate team.

Chu lauded Gregoire, a Democrat who served as governor of Washington state from 2005 until mid-January and is long-time backer of President Barack Obama.

"I am especially appreciative of Governor Gregoire for her trust and support over the past six months," Chu said in a lengthy resignation letter on Friday.

Chu worked with Gregoire on the clean-up of the Hanford site in Washington, one of the U.S. nuclear weapons development facilities.

Working on the nuclear waste issue with Gregoire and others has taken about five to 10 hours per week of his time over the last six months, Chu said in the letter.

Gregoire, 65, has worked on nuclear waste issues for decades. As a deputy state attorney general in the mid 1980s, Gregoire lobbied the federal government to disclose any health risks from contamination at Hanford.

Sources close to Gregoire say she has been vetted by the White House as a possible choice for a number of posts, including energy secretary, interior secretary and Environmental Protection Agency administrator.

Gregoire was an early supporter of Obama in his first White House race, and in doing so broke with Washington's U.S. senators, Patty Murray and Maria Cantwell, who supported Hillary Clinton.

In his letter, Chu said the Energy Department made "historic progress" in cleaning nuclear contamination left from Cold War weapons development.

"Despite this progress, the environmental clean-up projects still have considerable technical and project management challenges," he added.

Millions of gallons of toxic radioactive waste are stored in underground tanks at Hanford, a possible threat to the nearby Columbia River, which runs between Oregon and Washington State.

Security at the government's nuclear facilities would also fall to Gregoire if she became energy secretary.

During Chu's tenure, the Energy Department suffered an embarrassment when an 82-year-old nun and two peace activists broke into the government's maximum security facility for weapons grade uranium in Oakridge, Tennessee.